FAA Finalizes Steps For Pratt-Powered 777 Service Return
WASHINGTON—The FAA has finalized rules mandating inspections and modifications for Pratt & Whitney-powered Boeing 777s, completing a year-long process to develop fixes that address issues spotlighted in three engine failures and get grounded aircraft back into service.
Airworthiness directives (ADs) set for publication in the Federal Register by March 11 spell out new fan blade inspection protocols as well as engine nacelle modifications and inspections. The protocols follow proposed steps developed during the last year by Boeing, Pratt and the FAA, and outlined in late December 2021 draft directives.
The new fan blade check program adds ultrasonic inspections to Pratt’s existing, proprietary thermal acoustic imaging (TAI) method. Under the revised protocol, ultrasonic checks of each blade’s flow path region—the area nearest the blade root—are required every 275 flight cycles (FC), while inspections of two “mid-span” areas farther out from the root are done every 550 FC. In addition, all blades undergo a TAI every 1,000 FC.
Nacelle work includes inlet modifications that add “ballistic shielding and support structure to the inlet outer barrel, revising the outer cowl aft row fasteners, adding support structures to the aft bulkhead, and revising the inlet attach-ring to A-flange engine bolts and associated barrel nuts,” the FAA’s draft directive explained. Operators also must install thrust reverser debris shields, inspect fan cowl doors for moisture ingression, and conduct “functional checks” of hydraulic pump shutoff values “to ensure they close in response to the corresponding engine fire handle input,” the FAA said.
Each of the three events started when a fan blade—specifically a first-stage low-pressure compressor [LPC] blade on the PW4000 series—fractured due to fatigue cracking near the blade root, sending pieces of the blade into the nacelle’s forward inner surfaces and triggering a chain reaction that saw debris hit parts of the airframe and wings. The events—two involving United Airlines 777-200s, in February 2018 and February 2021, and one on a Japan Air Lines 777-200 in December 2020—called attention to unrecognized risks of airframe damage caused by parts of the nacelle breaking away as part of a “fan blade out” scenario.
The FAA and manufacturers worked for months to develop specific changes for the affected 777 fleet, and the regulator is re-examining its certification rules that emphasize ensuring fractured blades do not get ejected through the sides of the nacelle and into the airframe or wings.
The global fleet of Pratt-powered 777s totaled about 130 when the grounding occurred following the February 2021 event. Many of them—52—are with United Airlines. The U.S. carrier plans to work its Pratt-powered 777s back into its network right away, while several operators have accelerated plans to retire their affected airframes.